1. Field of the Invention
The present invention relates to a sonar transducer system for image formation.
2. Discussion of Background
An image forming sonar is a sonar device operating at a frequency of a few megahertz for visualizing objects placed on the sea bed. It replaces a television camera when the water is too cloudy. An important part of such a sonar is the transducer transmitting and receiving system. This transducer system must provide a wide sector of observation with high resolution.
A known transducer system has a single receiving antenna and a single transmitting antenna which covers the whole sector of observation with sound. The reception channels are preformed electronically and for each channel a different delay must be provided for each transducer signal. To cover for example a sector of observation of 45.degree. lateral deflection with a beam having a lateral width of 0.6.degree., 75 channels must be formed, which would require a very expensive electronic processing circuit. Furthermore, the sonar system has a reduced antenna gain with respect to a directional antenna system which causes an increase in the electric power required for its use.
It is also known to preform channels geometrically by using as many antennae as there are channels and by staggering them angularly by the desired value (0.6.degree.) for the above mentioned example. For a large number of channels, this technique becomes too expensive.
Finally, it is also known not to preform channels and to cover the space with sound by a mechanical sweep using a single pair of transmitting and receiving antennae effecting an alternate sweep; however, then the rate of image formation is insufficient.